Optical scanning apparatus and image forming apparatus

ABSTRACT

A housing ( 30 ) includes a base portion ( 30   a ) for installation of an optical beam emission unit ( 31 ), a light guiding unit ( 35   a - 39   a,    35   b - 39   b ), and a deflection unit ( 32, 33 ), and a cover portion ( 30   b   , 30   c ) that includes an indented heat emission channel ( 30   b   1, 30   c   1 ) that transmits heat in an inner portion of the housing ( 30 ) to a fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a non-provisional application claiming priority toand the benefit of Japanese Patent Application No. 2009-297259, filedDec. 28, 2009, Japanese Patent Application No. 2009-271156, filed Nov.30, 2009. The entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical scanning apparatus and animage forming apparatus.

2. Description of the Related Art

In an image forming apparatus such as a copying machine, a printer, amultifunction peripheral, or the like, a photosensitive member has asurface that is uniformly charged by a charging device and is opticallyscanned by an optical scanning apparatus to thereby form anelectrostatic latent image on its surface in response to imageinformation. Thereafter the electrostatic latent image is developed by adeveloping device using toner as a developing agent and is visualized asa toner image. The toner image is transferred onto a sheet with atransfer device and fixed onto the sheet by heating and pressure by afixing device. A series of image forming operations is completed bydischarge from the apparatus of the sheet with the toner image fixedthereto.

Conventionally, an optical scanning apparatus which is a principalconstituent component of an image forming unit incorporated into animage forming apparatus such as a copying machine, a printer, amultifunction peripheral, or the like has a housing including aninternal space having a predetermined volume. This housing accommodatesoptical components and the like such as a scanning optical system or thelike including a plurality of reflective mirrors that returnconstant-speed scanning light and guide the light to the photosensitivemember, such as an optical beam generating device that generates opticalbeams (laser light) (optical beam emission unit), a polygon mirrorformed by a hexagon or the like that deflects the light beams emittedfrom the optical beam generating device, a polygon motor that rotatesand drives the polygon mirror (polygon scanner motor), a control boardthat mounts electronic components including an IC and supports thepolygon motor, and an imaging lens (fθ lens) that images (converts toconstant-speed scanning light) the optical beams deflected by thepolygon mirror onto the photosensitive member.

However the polygon motor mounted on the control board produces heatwhen driven. The inner portion of the housing is heated by the heatproduced by the polygon motor and therefore the various componentsdisposed in the housing inner portion are affected by the heat.Therefore a heat strategy is typically adopted in an optical scanningapparatus. For example, a method of cooling the inner portion of thehousing has been disclosed in which a draft air duct for enabling airflow is formed in the housing to thereby allow heat in the inner portionof the housing to escape to the outside through the draft air duct.

Alternatively, an optical scanning apparatus in which a singledeflection device is disposed in a center of the housing to therebydeflect and allocate the optical beams in two symmetrical directionswith the deflection device has been proposed.

Alternatively, an optical scanning apparatus has been proposed in whichtwo housings (optical chambers) are disposed in parallel and scanrespective light beams in two symmetrical directions about thedeflection device. According to this optical scanning apparatus, sincethe size of one of the housings is reduced, positional deviation of thescanning line is effectively suppressed and problems associated withcolor shift are suppressed. Alternatively, the effect on color shiftcaused by the return mirror can be reduced by making the number ofreturn mirrors take a value of one.

However the optical beam generating device, the polygon motor, theoptical components and the like are disposed in the housing. When adraft air duct is formed randomly as an indentation with respect to theabove type of housing, there is a risk that localized thermaldeformation may increase as a result of large change in the shape of thehousing from a square shape, and that the installation region for theoptical beam generating device, the polygon mirror, the opticalcomponents, and the like will be subjected to a high degree of warping.When warping occurs in the installation region for the optical beamgenerating device, the polygon mirror, the optical components, and thelike in the housing, those components become inclined and light beamscan no longer be suitably guided.

Alternatively, since the above configuration requires that two lightbeams scan in one direction, the two light beams must be separated andguided to the photosensitive member and therefore a space with respectto the height direction in the housing must be ensured. Consequently,problems arise in relation to the increased size of the housing.Alternatively, a large width must be ensured in a height direction ofthe imaging lens provided for constant-speed scanning of the two lightbeams, and this causes cost increases. The size of the housing isfurther increased due to the fact that four optical systems for scanningfour light beams are all contained in a single housing.

Alternatively, in the above optical scanning apparatus, since theoptical path only returns once from the deflection device to thephotosensitive member, there is the problem that there is an increase inthe width in the height direction of the housing. In particular, when animaging lens with a long focal length is used, the housing size isincreased since the height of the housing increases proportional to thefocal length.

Consequently, the thermal deformation amount of the housing due totemperature fluctuation increases, the scanning position of opticalbeams deviates and therefore tends to result in problems in relation tocolor shift.

SUMMARY OF THE INVENTION

The present invention, conceived to address the above-mentioned problem,is designed to enable reduction in size of an optical scanning apparatusand to suppress failure of light guiding of optical beams resulting fromthermal deformation in a housing.

In order to solve the above-mentioned problem, an optical scanningapparatus of the present invention may include an optical beam emissionunit that emits an optical beam, a light guiding unit that guides theoptical beam, a deflection unit that deflects the optical beam, and achamber-shaped housing that accommodates the optical beam emission unit,the light guiding unit, and the deflection unit. The housing includes abase portion for installation of the optical beam emission unit, thelight guiding unit, and the deflection unit, and a cover portion thatincludes an indented heat emission channel that transmits heat in thehousing to a fluid.

According to this aspect of the present invention, the housing includesthe base portion enabling installation of the optical beam emissionunit, the light guiding unit and the deflection unit, and a coverportion including the indented heat emission channel that transmits theheat in the housing to the fluid. Therefore thermal deformation in thehousing resulting from the heat emission channel is concentrated in thecover portion and the effect on the base portion which installs theoptical beam emission unit, the light guiding unit and the deflectionunit can be reduced. Therefore according to this aspect of the presentinvention, light-guiding failure of the optical beams in the opticalscanning apparatus caused by thermal deformation of the housing can besuppressed.

According to this aspect of the present invention, since the opticalbeams deflected by the deflection device are returned by the reflectivemirror and travel along the upper surface and the lower surface of thebase plate of the housing, the width of the housing with reference to adirection of height can be effectively suppressed and therefore enablesdownsizing of the housing.

In order to solve the above-mentioned problem, an optical scanningapparatus may accommodate a scanning optical system in the housing. Thescanning optical system may include a deflection device that deflectsthe optical beams emitted from a light source, an imaging lens thatconverts the optical beams deflected by the deflection device toconstant-speed scanning light, and a first, second and third reflectivemirror returning the constant-speed scanning light and guiding the lightto the photosensitive member. The housing of the optical scanningapparatus may form a base plate that partitions the housing into anupper and a lower portion. The deflection device, and the firstreflective mirror and the imaging lens of the scanning optical systemmay be disposed on one surface of the base plate along the direction ofpropagation of the optical beams. The second and third reflectivemirrors of the scanning optical system may be disposed on the othersurface of the base plate along the direction of propagation of theoptical beams. A first opening may be formed between the imaging lensand the first reflective mirror on an optical path connecting thephotosensitive member with the third reflective mirror on the base plateabove. A second opening may be formed on the optical path connecting thefirst reflective mirror with the second reflective mirror on the baseplate.

According to this aspect of the present invention, since two opticalscanning apparatuses that can optically scan two photosensitive membersat the same time are disposed in parallel on a color image formingapparatus, a total of four photosensitive members can be opticallyscanned by optical beams corresponding to four-color (magenta, cyan,yellow and black) image information. However since a first opening isformed between the imaging lens and the first reflective mirror on anoptical path connecting the third reflective mirror and thephotosensitive member on the base plate formed on the housing of eachoptical scanning apparatus, a substantially uniform pitch is enabledbetween the four photosensitive members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a schematic configuration of acopying machine.

FIG. 2 is a sectional view showing the schematic configuration of alaser scanning unit provided in the copying machine.

FIG. 3 is a lower view of a laser scanning unit provided in the copyingmachine.

FIG. 4 is a sectional view showing the schematic configuration of alaser scanning unit provided in the copying machine.

FIG. 5 is a sectional view of an image forming apparatus (color laserprinter).

FIG. 6 is a sectional view of the main scanning of a single opticalscanning apparatus.

FIG. 7 is a sectional view of the main scanning of two optical scanningapparatuses.

FIG. 8 is a sectional view of the main scanning of two optical scanningapparatuses according to a reference example.

FIG. 9 is a sectional view of the main scanning of two optical scanningapparatuses according to a reference example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of an optical scanning apparatus and an image formingapparatus will be described below referring to the figures. In thefigures below, the dimensions of each member has been suitably varied tothereby show each member in a size that enables recognition. In thefollowing description, an example of an image forming apparatusaccording to the present invention will be described with reference to acopying machine.

FIG. 1 is a sectional view showing a schematic configuration of acopying machine P according to the present embodiment. As shown in thefigure, the copying machine P according to the present embodimentincludes an image reading unit 1 for reading an image of a document anda printing unit 2 that performs printing onto a recording sheet(recording medium) based on the read image data.

The image reading unit 1 illuminates light onto the image of thedocument to thereby read the image of the document as image data byreceiving the reflected light and includes a light source apparatus thatilluminates light onto the document or a light-receiving sensor or thelike that converts return light from the document.

The printing unit 2 includes a belt unit 6, an image forming unit 7, asheet cassette 8, a paper feed tray 9, a secondary transfer unit 10, afixing unit 11, a paper discharge tray 12, and a feed conveyance path13.

The belt unit 6 transfers the toner image formed on the image formingunit 7 and conveys the transferred toner image. The belt unit 6 includesan intermediate transfer belt 61 on which the toner image is transferredfrom the image forming unit 7, an endlessly forwarding drive roller 62linked to the intermediate transfer belt 61, a driven roller 63 and atension roller 64. The intermediate transfer belt 61 is configured bystretching across the drive roller 62, the driven roller 63, and tensionroller 64. The drive roller 63 is connected to a drive unit thatincludes a drive source such as a motor or the like, and rotates andimparts a gripping force to the intermediate transfer belt 61. Thedriven roller 63 rotates by being rotated and driven by the drive roller62. The tension roller 64 is a type of driven roller that is rotated anddriven by being driven by the rotations of the drive roller 62, andincludes a resilient mechanism to thereby apply a tension to theintermediate transfer belt 61. Furthermore the belt unit 6 also includesa cleaning unit (not shown) which is configured to remove residual tonerand the like from the intermediate transfer belt 61.

An image forming unit 7 is provided corresponding respectively to thecolors yellow (Y), magenta (M), cyan (C), and black (BK), and forms atoner image in each color. These image forming units 7 are arrayed alongthe intermediate transfer belt 61. Each image forming unit 7 has aphotosensitive member 71, a charging device 72, a laser scanning unit 73(optical scanning apparatus), a developing device 74, a primary transferroller 75, a cleaning apparatus 76, and a neutralization apparatus (notshown). The photosensitive member 71 is formed as a cylinder and a tonerimage is formed on the periphery of the photosensitive member 71 basedon an electrostatic latent image. The charging device 72 is opposed tothe photosensitive member 71 and places the peripheral face of thephotosensitive member 71 into a charged state. The laser scanning unit73 scans laser light that is emitted based on the printing format forthe image data on the peripheral surface of the charged photosensitivemember 71. The developing device 74 develops the toner image based onthe electrostatic latent image on the peripheral surface of thephotosensitive member 71 by supply of toner to the peripheral surface ofthe photosensitive member 71. The primary transfer roller 75 is opposedto the photosensitive member 71 to sandwich the intermediate transferbelt 61 and thereby executes primary transfer of the toner imagedeveloped by the photosensitive member 71 into the intermediate transferbelt 61. The cleaning apparatus 76 removes residual toner from thephotosensitive member 71 after primary transfer.

The sheet cassette 8 is freely detachable from the apparatus main bodyand contains recording paper. The paper feed tray 9 opens and closesfreely with respect to the apparatus main body and contains therecording paper. The secondary transfer unit 10 executes secondarytransfer of the image formed on the intermediate transfer belt 61 ontothe recording body and is configured from the drive roller 62 that isdriven by the intermediate transfer belt 61 and the secondary transferroller 10 a that is opposed to the drive roller 62 to sandwich theintermediate transfer belt 61. The fixing unit 11 fixes the toner imagethat is subjected to secondary transfer on the recording body onto therecording paper, and includes a heating roller that fixes the tonerimage onto the recording paper by pressure and heating. The feedconveyance path 13 includes a pick-up roller 13 a that conveys therecording paper from the sheet cassette 8, a paper feed roller 13 b thatconveys the recording body, and a discharge roller 13 c that dischargesthe recording body to the paper discharge tray 12.

As described above, the copying machine P according to the presentembodiment that has the above type of configuration acquires image databy the image reading unit 1, and the printing unit 2 performs printingoperations onto the recording paper based on the image data.

Next, the laser scanning unit (LSU) 73 in the copying machine Paccording to the present embodiment will be described with reference toFIG. 2 and FIG. 3. The laser scanning unit 73 as described above isprovided respectively in accordance to each color of yellow (Y), magenta(M), cyan (C), and black (BK). In the present embodiment, the apparatusis downsized by integrating the laser scanning unit 73 that is providedfor yellow (Y) and the laser scanning unit 73 that is provided formagenta (M) to form the laser scanning unit 73 a and integrating thelaser scanning unit 73 that is provided for cyan (C) and the laserscanning unit 73 that is provided for black (BK) to form the laserscanning unit 73 b. The laser scanning units 73 a and 73 b have the sameconfiguration and therefore the following description will only describethe laser scanning unit 73 a. FIG. 2 is a sectional view of the laserscanning unit 73 a and FIG. 3 is a lower view of the laser scanning unit73 a.

The laser scanning unit 73 a includes a housing 30, an optical beamgenerating device 31 (optical beam emission unit), a polygon mirror 32,a polygon motor 33, a control board 34, and optical components 35 a-39a, 35 b-39 b. In the present embodiment, the light beams are deflectedby the polygon mirror 32 and the polygon motor 33. In other words, thedeflection unit in the present embodiment is configured from the polygonmirror 32 and the polygon motor 33. In the present embodiment, the lightbeams are guided by the optical components 35 a-39 a, 35 b-39 b. Inother words, the guiding unit in the present embodiment is configuredfrom optical components 35 a-39 a, 35 b-39 b.

The housing 30 is formed from synthetic resin in an empty box-shape, andas shown in FIG. 2, includes the base portion 30 a, the upper cover 30 b(cover portion), and the lower cover 30 c (cover portion).

The base portion 30 a includes the optical beam generating device 31, apolygon mirror 32, a polygon motor 33, a control board 34, and opticalcomponents 35 a-39 a, 35 b-39 b, and upper end and lower end thereof areopened. Furthermore the upper cover 30 b closes the upper end of thebase portion 30 a and the lower cover 30 c closes the lower end of thebase portion 30 a. The upper cover 30 b and the lower cover 30 c includeindented heat emission channels 30 b 1, 30 c 1 that transfer heat in thelower inner portion of the housing 30. In other words, the copyingmachine P according to the present embodiment disposes the covers (theupper cover 30 b and the lower cover 30 c) with reference to the top andthe bottom of the base portion 30 a, and each cover (the upper cover 30b and the lower cover 30 c) includes the heat emission channels 30 b 1,30 c 1.

More precisely, the base portion 30 a is configured by integrating ahousing base plate 30 d, which is divided into two on the upper andlower portions of the inner portion of the housing 30, and a side wall30 e of the housing 30. Slits 30 a 1, 30 a 2 allowing passage of opticalbeams reflected by the optical components 36 a, 36 b (reflectivemirrors) are respectively disposed in proximity to the right and leftside walls 30 e of the housing base plate 30 d.

The upper end of the base portion 30 a is covered by an upper cover 30b, and the lower end of the base portion 30 a is covered by the lowercover 30 c. An indented heat emission channel 30 c 1 is formed along theentire portion of the lower cover 30 c (in FIG. 3, the entire portionfrom the upper end to the lower end) passing through the central portionon the outer side of the lower cover 30 c. The most depressed portion ofthe heat emission channel 30 c 1 (the upper end of the heat emissionchannel 30 c 1 in FIG. 2) is configured to come into contact with thebottom surface of the housing base plate 30 d. Furthermore slits 30 c 2,30 c 3 are respectively provided to allow passage of light beamsreflected by the optical components 39 a, 39 b (reflective mirror) asdescribed hereafter in proximity to the heat emission channel 30 c 1. Inother words, the housing 30 uses the housing base plate 30 d to form anupper chamber X on an upper side thereof and lower chambers Y1, Y2divided into two by the heat emission channel 30 c 1 is formed on alower side of the housing base plate 30 d.

Herein, the housing 30 is divided into two upper and lower portions bythe housing base plate 30 d. However when the laser scanning unit 73 ashown in FIG. 2 is provided vertically by rotating through 90 degrees,the housing base plate 30 d divides the housing 30 into right and leftportions. Therefore as used herein “the housing is divided into upperand lower portions” in this embodiment of the present invention meansthat the housing 30 is simply divided into two.

The optical beam generating device 31 is fixed to the housing 30, and isfixed to the side wall 30 e of the base portion 30 a that is positionedon the inner side of the face of the paper in FIG. 2. The optical beamgenerating device 31 illuminates light beams towards the polygon mirror32 that is provided in the housing 30.

The polygon mirror 32 deflects light beams emitted from the optical beamgenerating device 31, and is formed as a polygon (in the example shownin the figure, a hexagon is shown). The outer periphery of the polygonmirror 32 is formed by reflective mirror, and the central positionthereof is mounted by passing through the rotation shaft of the polygonmotor 33.

The polygon motor 33 rotates and drives the polygon mirror 32, and forexample is configured by a precision motor formed from a DC brushlessmotor or the like. The polygon motor 33 is installed on the controlboard 34.

The control board 34 is formed from a plate member including metal andhas a planar shape in a rectangular shape. The control board 34 is fixedat the four corners thereof via a machine screw (not shown) so that therear surface thereof comes into contact with an upper surface of thehousing base plate 30 d. Furthermore the polygon motor 33 is fixed tothe surface side (the upper side) of the control board 34. Althoughomitted from FIG. 2, an electronic component such as a driving IC or thelike for the polygon motor 33 is mounted on the surface of the controlboard 34. The control board 34 is provided in a central portion of theupper surface of the housing base plate 30 d due to the relationship inwhich the polygon mirror 32 is provided in a central portion of theupper surface of the housing base plate 30 d.

The optical components 35 a, 35 b of the optical components 35 a-39 a,35 b-39 b are an imaging lens (fθ lens) provided in the upper chamber X,operate to focus the light beams illuminated from the polygon mirror 32and are disposed on the right and the left with the polygon mirror 32 inthe center. The optical components 36 a, 36 b are reflective mirrors,and are provided respectively on an outer side of the optical components35 a, 35 b to thereby respectively guide light beams emitted from thepolygon mirror 32 through the slits 30 c 2, 30 c 3 into the lowerchambers Y1, Y2. The optical components 37 a, 37 b are reflectivemirrors provided respectively in the lower chambers Y1, Y2 and areconfigured to enable illumination of light beams guided through theslits 30 a 1, 30 a 2 into the lower chambers Y1, Y2. The opticalcomponents 38 a, 38 b are long lenses provided respectively in the lowerchambers Y1, Y2, and are provided respectively more towards an innerside (the side of the heat emission channel 30 c 1) than the opticalcomponents 37 a, 37 b. These optical components 38 a, 38 b operate toenable uniform illumination without magnification differences of lightbeams illuminated respectively from the optical components 37 a, 37 bonto the photosensitive member 71. The optical components 39 a, 39 b arereflective mirrors, are provided more towards an inner side than theoptical components 38 a, 38 b (the heat emission channel 30 c side) tothereby emit the light onto the photosensitive member 71 through theslits 30 c 2, 30 c 3.

The optical components 35 a-39 a, 35 a-39 b in the present embodimentare provided to extend in the same direction and extend in the samedirection as the heat emission channel 30 b 1, 30 c 1.

Furthermore as shown in FIG. 1, the copying machine P in the presentembodiment includes a fan apparatus 14 that flows air into the heatemission channel 30 b 1 of the upper cover 30 b, and a fan apparatus 15that flows air into the heat emission channel 30 c 1 of the lower cover30 c. In the present embodiment, as shown in FIG. 2, these fanapparatuses 14, 15 form an air flow a1 inwardly from the front of thepage in the heat emission channel 30 b 1 of the upper cover 30 b, and anair flow a2 is formed towards the front from the inner part of the pagein the heat emission channel 30 c 1 of the lower cover 30 c. That is tosay, in the present embodiment, the direction of flow of the air flow a1flowing towards the heat emission channel 30 b 1 of the upper cover 30 bis opposite to the direction of flow of the air flow a2 flowing towardsthe heat emission channel 30 c 1 of the lower cover 30 c.Conventionally, a copying machine may include a fan apparatus forcooling the photosensitive member 71 or the like. In this case, eitherof the fan apparatuses 14, 15 may be incorporated into the existing fanapparatus. In this manner, the number of installations of the fanapparatus may be decreased thereby enabling downsizing of the copyingmachine.

The laser scanning unit 73 a, 73 b configured in this manner emits lightbeams from the optical beam generating device 31 based on image data.The light beams are illuminated onto the polygon mirror 32. The opticalbeams that illuminated onto the polygon mirrors 32 are scanned byrotation of the polygon mirror 32. The scanned light beams are guidedonto the photosensitive member 71 through the optical components 35 a,35 b (fθ lens), the optical components 36 a, 36 b (reflective mirror),the optical components 37 a, 37 b (reflective mirror), the opticalcomponents 38 a, 38 b (elongated lens), and the optical components 39 a,39 b (reflective mirror). An electrostatic latent image is formed on thephotosensitive member 71 by the emitted light beams based on thedetection signal for determining the write start position of the imageon the photosensitive member 71.

The housing 30 of the laser scanning unit 73 provided in the copyingmachine P according to the present embodiment includes a base portion 30a that is provided with the optical beam generating device 31, thepolygon mirror 32, the polygon motor 33, the control board 34, and theoptical components 35 a-39 a, 35 b-39 b, and the cover portion (uppercover 30 b, lower cover 30 c) that is provided with the indented heatemission channel 30 b 1, 30 c 1 to transfer heat in the housing 30 tothe air flow a1, a2. As a result, the heat deformation of the housing 30resulting from the heat emission channel 30 b 1, 30 c 1 is concentratedin the cover portion (upper cover 30 b, lower cover 30 c), and thereforethe effect is decreased on the base portion 30 a on which the opticalbeam generating device 31, the polygon mirror 32, the polygon motor 33,the control board 34, and the optical components 35 a-39 a, 35 b-39 bare installed. Therefore, the laser scanning unit 73 provided in thecopying machine P according to the present embodiment enablessuppression of light-guiding failure of light beams resulting fromthermal deformation of the housing 30.

The laser scanning unit 73 that is provided in the copying machine Paccording to the present embodiment provides respective cover portions(upper cover 30 b, lower cover 30 c) above and below the base portion 30a, and each cover portion (upper cover 30 b, lower cover 30 c) isprovided with a heat emission channel 30 b 1, 30 c 1. Consequently, heatin the housing 30 can be radiated from both upper and lower directions,and therefore heat in the housing can be more effectively radiated tothe outside.

In the above embodiment, a single polygon mirror 32 and a polygon motor33 deflect light beams emitted from two optical beam generating devices31. As a result, in comparison with providing a polygon mirror andpolygon motor respectively for each light beam emitted from the opticalbeam generating device 31, the number of polygon mirrors and polygonmotors can be reduced. Furthermore according to the present embodiment,the polygon mirror 32 and polygon motor 33 can be disposed in the centerof the base portion 30 a, and therefore the heat emission channel 30 b1, 30 c 1 can be formed above and below the polygon mirror 32 andpolygon motor 33. Consequently, heat can be radiated from both above andbelow the polygon mirror 32 and polygon motor 33, and therefore enablingmore efficient radiation of heat in the housing 30 to the outside.

In the present embodiment, the inner portion of the housing 30 isdivided by the heat emission channel 30 c 1 into the region guiding thelight beams emitted from one of the optical beam generating devices 31(lower chamber Y1) and the region guiding the light beams emitted fromthe other optical beam generating device 31 (lower chamber Y2).Consequently, there is no need to separately provide a partition toseparate into two regions (lower chamber Y1 and lower chamber Y2), andconsequently, the material forming the housing can be reduced.

In the laser scanning unit 73 provided in the copying machine Paccording to the present embodiment, heat emission channels 30 b 1, 30 c1 are provided extending in the same direction, and therefore thedirection of flow of the air flow a1, a2 with respect to each heatemission channel 30 b 1, 30 c 1 is opposite. Consequently, cold air flowfrom both sides flows into the heat emission channel 30 b 1, 30 c 1 inthe direction of extension of the heat emission channel 30 b 1, 30 c 1,and therefore uniform cooling of the laser scanning unit 73 is enabled.

Furthermore the optical components 35 a-39 a, 35 b-39 b in the laserscanning unit 73 provided in the copying machine P according to thepresent embodiment extend in the same direction, and extend in the samedirection as the heat emission channel 30 b 1, 30 c 1. As a result, theair flow a1, a2 flows along the optical components 35 a-39 a, 35 b-39 b,and enables suppression of the thermal deformation of the opticalcomponents 35 a-39 a, 35 b-39 b for all of the optical components 35a-39 a, 35 b-39 b.

Another embodiment according to the present invention will be describedbelow. Those portions that are the same as those in the embodimentsabove are omitted from the following description for the sake ofsimplicity.

FIG. 4 is a sectional view showing the schematic configuration of alaser scanning unit 73 a according to the present embodiment. As shownin the figure, the laser scanning unit 73 a in the copying machine Paccording to the present embodiment is disposed in the heat emissionchannel 30 c 1, and is provided with a heat transfer fin 40 (heattransfer unit) to transfer heat from the polygon motor 33 to the heatemission channel 30 c 1. The heat transfer fin 40 is configured by aplurality of fan members which extend to the flow direction of the airflow a1 in the heat emission channel 30 c 1 (to the longitudinaldirection of the heat emission channel 30 c 1) and are installed tostand substantially perpendicular to the flow direction (substantiallyparallel to the side wall face of the heat emission channel 30 c 1).

The provision of the heat transfer fin 40 in this manner increases thesurface area with respect to the air flow a1 and enables effectiveradiation of heat from the polygon motor 33 to the heat emission channel30 c 1.

Next, another embodiment of the present invention will be describedmaking reference to the attached figures.

FIG. 5 is a sectional view of a color laser printer according to anembodiment of an image forming apparatus of the present invention. Thecolor laser printer in the figure is a tandem type printer, and amagenta image forming unit 101M, a cyan image forming unit 101C, ayellow image forming unit 101Y, and a black image forming unit 101K aredisposed at a fixed interval in tandem in a central portion in the mainbody 100 of the printer.

Photosensitive drums 102 a, 102 b, 102 c, 102 d are respectivelydisposed as photosensitive bodies on each of the image forming units101M, 101C, 101Y, 101BK. A charging device 103 a, 103 b, 103 c, 103 d, adeveloping device 104 a, 104 b, 104 c, 104 d, a transfer roller 105 a,105 b, 105 c, 105 d, and a drum cleaning apparatus 106 a, 106 b, 106 c,106 d are respectively disposed in the periphery of each photosensitivedrum 102 a-102 d.

The photosensitive drums 102 a-102 d are drum-shaped photosensitivebodies, and are rotated at a predetermined processing speed in thedirection of the arrow in the figure (clockwise direction) by a drivemotor (not shown). Alternatively, the charging devices 103 a-103 d applya uniform charge with a predetermined potential to the surface of thephotosensitive drum 102 a-102 d with a charging device that is chargedby a charging device power source (not shown).

The developing devices 104 a-104 d respectively contain magenta (M),toner, cyan (C) toner, yellow (Y) toner, and black (BK) toner, attachtoner of each color to each electrostatic latent image formed on eachphotosensitive drum 102 a-102 d, and visualize each electrostatic latentimage as toner images having respective colors.

Alternatively, the transfer rollers 105 a-105 d are disposed to enableabutment with each photosensitive drum 102 a-102 d through theintermediate transfer belt 107 with each primary transfer unit. Theintermediate transfer belt 107 is stretched between the drive roller 108and the tension roller 109 to thereby enable scanning on an uppersurface of each photosensitive drum 102 a-102 d. The drive roller 108 isdisposed to enable abutment with the secondary transfer roller 110though the intermediate transfer belt 107 at the primary transfer unit.Alternatively, a belt cleaning apparatus 111 is disposed in proximity tothe tension roller 109.

However toner containers 112 a, 112 b, 112 c, 112 d for replenishingtoner in each developing device 104 a-104 d are arrayed in a line aboveeach image forming unit 101M, 101C, 101Y, 101K in the printer main body100.

Alternatively, two optical scanning apparatuses 113 are disposed withrespect to the paper conveying direction below each image forming unit101M, 101C, 101Y, 101K in the printer main body 100, and a sheetcassette 114 is detachably disposed on the bottom portion of the printermain body 100 below the optical scanning apparatus 113. A plurality ofpaper sheets (not shown) is stacked and contained in the sheet cassette114. A pickup roller 115 for removing paper from the sheet cassette 114,a feed roller 116 for separating removed sheets and transferringindividual sheets to the conveyance path S, and a retard roller 117 areprovided in proximity to the sheet cassette 114.

Alternatively, a conveying roller pair 118 that conveys a sheet and aresist roller pair 119 that stands by for a predetermined period andsupplies paper at a predetermined timing to a secondary transfer unitthat is the abutment portion of the drive roller 108 with the secondarytransfer roller 110 are provided in the conveyance path S extendingvertically in the side portion of the printer main body 100. Anotherconveyance path S′ used when forming an image on both sides of a sheetis formed on the side of the conveyance path S, and a plurality ofreversing roller pairs 120 are provided at a suitable interval in theconveyance path S′.

However, the conveyance path S disposed vertically on one side portionin the printer main body 100 extends to the paper discharge tray 121provided on an upper surface of the printer main body 100. A fixingapparatus 122 and discharge roller pairs 123, 124 are provided along thepath S.

Next, the operation of image formation by the color laser printer havingthe above configuration will be described.

When an image formation start signal is produced, the respectivephotosensitive drums 102 a-102 d in the respective image forming units101M, 101C, 101Y, 101K are rotated at a predetermined process speed inthe direction of the arrow (clockwise direction) in the figure. Thesephotosensitive drums 102 a-102 d are uniformly charged by the chargingdevice 103 a-103 d. Respective optical scanning apparatuses 113 emitlight beams that are modulated by the color image signal for each color,those light beams are emitted to the surface of the respectivephotosensitive drums 102 a-102 d, and form respective electrostaticlatent images corresponding to the color image signals on the respectivephotosensitive drums 102 a-102 d.

Firstly magenta toner is attached to the electrostatic latent imageformed on the photosensitive drum 102 a of the magenta image formingunit 101M by the developing device 104 a to which the developing biasthat has the same polarity as the charged polarity of the photosensitivedrum 102 a is applied. That electrostatic latent image is thenvisualized as a magenta toner image. The magenta toner image issubjected to primary transfer onto the intermediate transfer belt 107that is rotated in the direction of the arrow in the figure by theaction of the transfer roller 105 a to which the primary transfer biasthat has the opposite polarity to the toner is applied in the primarytransfer unit (transfer nip portion) between the photosensitive drum 102a and the transfer roller 105 a.

In this manner, the intermediate transfer belt 107 on which the magentatoner image undergoes primary transfer is transferred to the cyan imageforming unit 101C. In the same manner as above, in the cyan imageforming unit 101C, the cyan toner image formed on the photosensitivedrum 102 b is transferred and superimposed on the magenta image on theintermediate transfer belt 107 in the primary transfer unit.

In the same manner thereafter, a yellow and a black image formedrespectively in the photosensitive drums 102 c, 102 d of the yellow andblack image forming units 101Y, 101K are sequentially superimposed inthe respective primary transfer units on the magenta and cyan tonerimage that is superimposed and transferred onto the intermediatetransfer belt 107, to thereby form a full-color toner image on theintermediate transfer belt 107. Residual toner remaining on thephotosensitive drums 102 a-102 d without being transferred onto theintermediate transfer belt 107 is removed by the drum cleaningapparatuses 106 a-106 d and therefore each photosensitive drum 102 a-102d is provided for use in the following image formation.

When the distal end of the full-color toner image on the intermediatetransfer belt 107 reaches the secondary transfer unit (transfer nipportion) between the drive roller 108 and the secondary transfer roller110, the sheet conveyed from the sheet cassette 114 to the pick-uproller 115, the feed roller 116 and the retard roller 117 are conveyedto the secondary transfer unit by the resist roller pair 119. Then afull-color toner image is subjected to secondary transfer in a singleoperation from the intermediate transfer belt 107 onto the sheetconveyed to the secondary transfer unit by the secondary transfer roller110 to which a secondary transfer bias that has an opposite polarity tothe polarity of the toner is applied.

The sheet receiving the transfer of the full-color toner image isconveyed to the fixing apparatus 122, and the full-color toner image isheat fixed onto the sheet by application of heat and pressure, and thenthe sheet with the fixed toner image is discharged into the paperdischarge tray 121 by the discharge roller pair 123, 124, to therebycomplete a series of image forming operations. Residual toner thatremains on the intermediate transfer belt 107 without transfer onto thesheet is removed by the belt cleaning apparatus 111 to thereby preparethe intermediate transfer belt 107 for the next image forming operation.

The optical scanning apparatus according to the present invention willbe described below making reference to FIG. 6 and FIG. 7. FIG. 6 is asectional view of the main scanning of a single optical scanningapparatus according to the present invention. FIG. 7 is a sectional viewof the main scanning of two optical scanning apparatuses according tothe present invention.

Since the basic configuration of the two optical scanning apparatuses inFIG. 7 is the same, the configuration of the single optical scanningapparatus 113 in FIG. 6 will be described. The optical scanningapparatus 113 has a housing 125 that is integrally formed from resin. Ahorizontal base plate 125A is integrally formed to partition the upperand lower inner portion of the housing 125. A polygon mirror 125 that isa deflection apparatus is disposed in a central portion of the uppersurface of the base plate 125A of the housing 125. Two scanning opticalsystems 130, 140 are disposed symmetrically on both sides about thepolygon mirror 126 on the upper and lower surfaces of the base plate125A in the housing 125.

The scanning optical systems 130, 140 are respectively provided with afirst imaging lens 131, 141 and a first reflective mirror 132, 142disposed along the direction of propagation of light beams on the uppersurface of the base plate 125A inside the housing 125 and a secondimaging lens 133, 143, a second reflective mirror 134, 144 and a thirdreflective mirror 135, 145 disposed along the direction of propagationof light beams on the lower surface of the base plate 125A. Althoughthis is not shown, the each scanning optical system 130, 140 is alsoprovided with a cylindrical lens, a collimator lens, and a laser diodeas a light source accommodated in the housing 125.

The single optical scanning apparatus 113 shown in FIG. 6 uses exposurelight to scan the photosensitive drum 102 a of the magenta image formingunit 101M and the photosensitive drum 102 b of the cyan image formingunit 101C shown in FIG. 5. In each scanning optical system 130, 140,respective first openings 136, 146 are formed on the optical pathconnecting the third reflective mirror 135, 145 and the photosensitivedrum 102 a, 102 b between the first imaging lens 131, 141 and the firstreflective mirror 132, 142, and second openings 137, 147 are formed onthe optical path connecting the first reflective mirror 132, 142 and thesecond reflective mirror 133, 143 of the base plate 125A.

Light beams that are emitted from the laser diode (not shown) that isprovided in each scanning optical system 130, 140 in this single opticalscanning apparatus 113 are concentrated into a linear optical flux bythe collimator lens, and a cylindrical lens (not shown) to becomeincident upon the rotated and driven polygon mirror 126 from twosymmetrical directions.

Each light beam that becomes incident upon the polygon mirror 126 isdeflected by the polygon mirror 126, and then is converted toconstant-speed scanning light by passing through the first imaging lens131, 141. The constant-speed scanning light is returned orthogonally ina downward direction by the first reflective mirrors 132, 142, passesthrough the second openings 137, 147 that are formed on the base plate125A, reaches the second reflective mirror 133, 143, returnsorthogonally by the second reflective mirrors 133, 143, and proceedshorizontally along the lower surface of the base plate 125A. Thereafterthe light beam passes through the second imaging lens 134, 144, reachesthe third reflective mirror 135, 145, is returned upwardly in anorthogonal direction by the third reflective mirrors 135, 145, passesthrough the first opening 136, 146 formed in the base plate 125A towardthe photosensitive drum 102 a, 102 b and therefore respectively exposesand scans the photosensitive drums 102 a, 102 b.

Although the single optical scanning apparatus 113 shown in FIG. 6exposes and scans the photosensitive drum 102 a of the magenta imageforming unit 101M and the photosensitive drum 102 a of the cyan imageforming unit 101C shown in FIG. 5, the color laser printer shown in FIG.5 includes two aligned optical scanning apparatuses 113 that are thesame as FIG. 7 to thereby use light beams to expose and scan all of thefour photosensitive drums 102 a-102 d including the yellow image formingunit 101Y and the black image forming unit 101 B K using the two opticalscanning apparatuses 113. In FIG. 7, the same reference numerals denotethe same elements configuring the two optical scanning apparatuses 113.

In the optical scanning apparatus 113, light beams that are deflected bythe polygon mirror 126 are returned by the first reflective mirror 132,142 and the second reflective mirror 133, 143 and proceed along theupper surface and lower surface of the base plate 125A of the housing125 and therefore enable a reduction in the width with respect to thedirection of height of the housing 125 as well as downsizing of thehousing 125 and downsizing of the overall optical scanning apparatus113.

In the present embodiment, since the two scanning optical systems 130,140 are disposed symmetrically on both sides about the polygon mirror126 in a central portion in the housing 125, the two photosensitivedrums 102 a and 102 b, or 102 c and 102 d, can simultaneously be scannedby the single optical scanning apparatus 113.

Since the two optical scanning apparatuses 113 that enable simultaneousscanning of the four photosensitive drums 102 a-102 d as described aboveare aligned on the color laser printer as shown in FIG. 5, the fourphotosensitive drums 102 a-102 d are scanned using light beams inaccordance with image information for the four colors (magenta, cyan,yellow and black). However since first openings 136, 146 are formedbetween the first imaging lens 131, 141 and the first reflective mirror132, 142 on the optical path connecting the third reflective mirror 135,145 and the photosensitive drums 102 a-102 d of the base plate 125Aformed on the housing 125 of each optical scanning apparatus 113, thepitch L, L′ between the four photosensitive drums 102 a-102 d can besubstantially equalized and the guiding distance for the return opticalpath on the lower surface of the base plate 125A can be used to amaximum.

As shown in FIG. 8, when the first openings 136, 146 are formed betweenthe polygon mirror 126 and the first imaging lenses 131, 141, the returnoptical path of the second reflective mirrors 133, 143 and the thirdreflective mirrors 135, 145 can be lengthened. However generally, it isoften the case that the first imaging lens 131, 141 is disposed inproximity to the polygon mirror 126, and consequently in thisconfiguration, the pitch L between the photosensitive drums 102 a and102 b and between 102 c and 102 d in each optical scanning apparatus113′ is reduced. For that reason, when both optical scanning apparatuses113′ are aligned in the conveying direction of the sheet as shown in thefigure, the pitch L′ between the photosensitive drums 102 b and 102 cincreases relative to the pitch L, and therefore equalization of thepitches L, L′ between the four colors photosensitive drums 102 a-102 dbecomes difficult.

The pitch L′ between the four colors photosensitive drums 102 b-102 cmay be reduced in order to equalize the pitches L, L′ between the fourphotosensitive drums 102 a-102 d. However the configuration shown inFIG. 9 must be adopted in order to reduce the pitch L′ between thephotosensitive drums 102 b-102 c. However the problem arises that thisconfiguration enlarges the housing 125 since the width D′ in a heightdirection of the housing 125 of each optical scanning apparatus 113″becomes greater than the width D of the optical scanning apparatuses113, 113′ shown in FIG. 7 and FIG. 8.

Although the embodiments of the present invention have been describedabove making reference to the attached figures, the present invention isnot limited to the embodiments. The shape of each constituent membershown in the above embodiments and the combination thereof is merelyexemplary, and various modifications are possible based on designrequirements within a scope that does not depart from the spirit of thepresent invention.

For example, in the embodiments above, a configuration in which a laserscanning unit 73 that is an example of the optical scanning apparatusaccording to the present invention is mounted a copying machine that isa single image forming apparatus. However the optical scanning apparatusaccording to the present invention is not limited to this configurationand may be mounted on devices such as measurement apparatuses,inspection apparatuses or the like in addition to an image formingapparatus such as a copying machine.

What is claimed is:
 1. An optical scanning apparatus comprising anoptical beam emission unit that emits an optical beam, a light guidingunit that guides the optical beam, a deflection unit that deflects theoptical beam, and a chamber-shaped housing that accommodates the opticalbeam emission unit, the light guiding unit, and the deflection unit,wherein the housing comprises a base portion for installation of theoptical beam emission unit, the light guiding unit, and the deflectionunit, and cover portions, each cover portion including a respectiveindented heat emission channel that transmits heat inside the housing toa fluid therein, and wherein the heat emission channels are disposed toextend along the same direction, and fluid moving devices cause thefluid in one heat emission channel to flow in an opposite direction tothe fluid in the other heat emission channel.
 2. The optical scanningapparatus according to claim 1 comprising a heat transmission unit thatis provided in the heat emission channel and transmits heat from thedeflection unit to the heat emission channel.
 3. The optical scanningapparatus according to claim 1 comprising a plurality of opticalcomponents that extend in the same direction as the light guiding unit,and the heat emission channel extends in the same direction as thedirection of extension of the optical components.
 4. The opticalscanning apparatus according to claim 1 wherein the deflection unitcomprises a polygon motor and a polygon mirror that deflects the opticalbeams emitted from the two optical beam emission units and are disposedin the center of the base portion, respective cover portions aredisposed on the top and the bottom of the base portion to thereby enableformation of a heat emission channel on the top and the bottom of thedeflection unit.
 5. The optical scanning apparatus according to claim 4wherein the inner portion of the housing is separated by the heatemission channel into a region in which optical beams emitted from oneof the optical beam emission units are guided and a region in which theoptical beams emitted from the other optical beam emission unit areguided.
 6. An image forming apparatus including an optical scanningapparatus that emits optical beams and scans, a photosensitive member onwhich an electrostatic latent image is formed by illumination with theoptical beams, and a developing device that forms a toner image bydeveloping the electrostatic image, and is provided with the opticalscanning apparatus according to claim 4 as an optical scanningapparatus.
 7. An optical scanning apparatus that accommodates a scanningoptical system in a housing, the scanning optical system includes adeflection device that deflects the optical beams emitted from a lightsource, an imaging lens that converts the optical beams deflected by thedeflection device to constant-speed scanning light, and a first, secondand third reflective mirror returning the constant-speed scanning lightand guiding the light to the photosensitive member, the housing of theoptical scanning apparatus forms a base plate that partitions thehousing into an upper and a lower portion, the deflection device, andthe first reflective mirror and the imaging lens of the scanning opticalsystem are disposed on one surface of the base plate along the directionof propagation of the optical beams, the second and third reflectivemirrors of the scanning optical system are disposed on the other surfaceof the base plate along the direction of propagation of the opticalbeams, a first opening is formed between the imaging lens and the firstreflective mirror on an optical path connecting the photosensitivemember with the third reflective mirror on the base plate, and a secondopening is formed on the optical path connecting the first reflectivemirror with the second reflective mirror on the base plate.
 8. Theoptical scanning apparatus according to claim 7 wherein two scanningoptical systems are disposed symmetrically about the deflection device.9. A color image forming apparatus wherein two optical scanningapparatuses according to claim 8 are disposed in parallel with respectto the direction of conveying of the sheet.